As examples of engine-driven low-speed vehicles which travel at relatively low speeds, there are golf carts, utility vehicles, and others, which are hereinafter collectively referred to as low-speed vehicles. In these low-speed vehicles, a transaxle reduces the speed of a driving power of the engine and rotates its axles with the reduced speed. The transaxle also has a rearward travel function and is configured to be able to switch between forward travel and rearward travel by switching a shift sleeve.
A driving unit which is typically equipped in a low-speed vehicle, for example, a golf cart, will be described with reference to FIG. 3B. FIG. 3B is a plan view showing in perspective a driving system for a golf cart 51. Turning now to FIG. 3B, the golf cart 51 is equipped with front wheels 60 which are positioned at a front portion (upper side in FIG. 3B) of a vehicle body thereof and is configured to be operated by a handle 59, and rear wheels 61 which are positioned at a rear portion of the vehicle body and is configured to be driven by an output shaft 55 of an engine 54. In the golf cart 51, the engine 54 and a transaxle 57 are respectively arranged forward and rearward in a narrow space between vehicle frames 53 under a seat 52. A driving power of the output shaft 55 of the engine 54 is transmitted to an input shaft 58 of the transaxle 57 located rearward via a continuously variable transmission (CVT) 56 which is a power transmission system mounted on a right side of the engine 54. In this configuration, the input shaft 58 of the transaxle 57 is driven to be rotated in the same direction as the output shaft 55 of the engine 54.
FIG. 4 is an exploded cross-sectional view showing a conventional mechanical reduction gear transaxle 161, which is one type of the above described transaxle for the engine-driven low speed vehicle. The mechanical reduction gear transaxle 161 is provided with an intermediate shaft 64 between an input shaft 62 and axles 63, and an idle shaft 65 for rearward travel between the input shaft 62 and the intermediate shaft 64. The transaxle 161 is configured in such a manner that a shift sleeve 68 switches between a forward travel gear mechanism 66 mounted between the input shaft 62 and the intermediate shaft 64 and a rearward travel gear mechanism 67 mounted between the input shaft 62 and the idle shaft 65, enabling the axles 63 to be rotated for forward travel or for rearward travel. In FIG. 4, arrows illustrated on the right side of the transaxle 161 indicate rotational directions of the respective shafts during rotation for forward travel. When the shift sleeve 68 is switched and coupled to the forward travel gear mechanism 66, the axles 63 are rotated clockwise when the transaxle 161 is viewed from rightward (from the input side of the input shaft 62) via a transmission gear mechanism 69 between the intermediate shaft 64 and the axle 63 so that the vehicle body travels forward. On the other hand, when the shift sleeve 68 is switched and coupled to the rearward travel gear mechanism 67, the axles 63 are rotated counterclockwise when the transaxle 161 is viewed from rightward via the transmission gear mechanism 69 between the intermediate shaft 64 and the axle 63 so that the vehicle body travels rearward. With this configuration, the axles 63 can be rotated clockwise when viewed from rightward of the transaxle 161 while speed reduction in forward travel is performed in a minimum of two stages by the forward travel gear mechanism 66 and the transmission gear mechanism 69.
To rotate the axles 63 clockwise in this configuration, the input shaft 62 is required to be rotated clockwise for forward travel. In this case, the output shaft 55 (FIG. 3B) of the engine 54 (FIG. 3B) configured to drive the input shaft 62 via the CVT 56 (FIG. 3B) needs to be rotated clockwise as well. For this reason, the transaxle 161 is incompatible with a general purpose engine whose output shaft 55 is rotated counterclockwise when the engine 54 is seen from the output shaft 55 side. Therefore, there arises a need for a special engine configured to be rotated clockwise, whose output shaft is rotated in the same direction as the input shaft 62 of the transaxle 161. In addition, since the transaxle 161 having the above configuration has four shafts consisting of the input shaft 62, the intermediate shaft 64, the rearward travel idle shaft 65, and the axles 63, a casing 70 having a sufficient size to accommodate these four shafts becomes necessary.
Under the circumstances, there has been a need for a transaxle configured to be driven by the general purpose engine whose output shaft is rotatable counterclockwise (to the left) when the engine is seen from the output shaft side, rather than the special engine whose output shaft is rotatable clockwise. FIGS. 5 and 6 are side views showing an example of a transaxle configured to be driven by the general purpose engine whose output shaft is rotatable counterclockwise (to the left) when the engine is seen from the output shaft side. As shown in FIGS. 5 and 6, a transaxle 71 for a vehicle includes two intermediate shafts 74 and 75 which are mounted between an input shaft 72 and axles 73 and is configured in such a manner that a shift sleeve 78 switches between a forward travel gear mechanism 76 and a rearward travel chain mechanism 77 mounted between the input shaft 72 and the intermediate shaft 74, causing the axles 73 to be rotated for forward travel or for rearward travel. Such prior art is disclosed in Japanese Laid-Open Patent Application Publication No. Hei. 2006-82662 or No. Sho. 62-234726.
In the configuration of FIG. 5, when the shift sleeve 78 is switched and coupled to the forward travel gear mechanism 76, counterclockwise rotation transmitted to the input shaft 72 is transmitted from the input shaft 72 to the intermediate shaft 74 and further to the intermediate shaft 75 via the transmission gear mechanism 79, and further from the intermediate shaft 75 to the axles 73 via a transmission gear mechanism 80 mounted between the intermediate shaft 75 and the axles 73, causing the axles 73 to be rotated clockwise when the transaxle 71 is seen from rightward in FIG. 5. Thereby, the vehicle travels forward. On the other hand, when the shift sleeve 78 is switched and coupled to the rearward travel chain mechanism 77, the rotation of the input shaft 72 is transmitted to the intermediate shaft 74 via the rearward travel chain mechanism 77 and further from the intermediate shaft 75 to the axles 73 via the transmission gear mechanism 80, causing the axles 73 to be rotated counterclockwise when the transaxle 71 is seen from rightward in FIG. 5. Thereby, the vehicle travels rearward. According to the transaxle 71 having the above configuration, the axles 73 can be rotated clockwise even though the input shaft 72 is rotated counterclockwise during forward travel as indicated by arrows in FIG. 5. However, two intermediate shafts 74 and 75 become necessary between the input shaft 72 and the axles 73 and hence a casing 81 having a size sufficient to accommodate the intermediate shafts 74 and 75 also becomes necessary.
As described above, in the low-speed vehicles such as the golf cart 51, the engine 54 and the transaxle 57 are typically mounted in a narrow space under the seat 52. Therefore, the engine 54 and the transaxle 57 have been expected to keep silent and have more compact configuration.
In order to achieve the silence in the above described mechanical gear reduction configuration, it is necessary to produce gears so that their tooth profile and tooth trace are precise. So, gear production has been time-consuming and expensive. Under these conditions, there has been a need for a transaxle which is capable of achieving silence while reducing a cost to be consumed for the gear production.
Furthermore, since the engine is limited in improving compactness, improving compactness of the transaxle is an important issue at present.
However, since both of the transaxle 161 and the transaxle 71 have four shafts as described above, the casings 70 and 81 having sizes sufficient to accommodate these four shafts become necessary. The low-speed vehicle into which the transaxle 161 or 71, which has such a large-sized casing 70 or 81, is mounted is forced to be designed with less flexibility.